During the build process, the Titanium Mobile and Titanium Desktop rubles are checked out from Github and inserted into the /bundles directory in the titanium.core plugin. However, it appears that even though the checkout works, the bundles go missing somewhere during the build. This can be confirmed by downloading the linked JAR files, renaming them to .zips, and looking in the /bundles directory.
This build has them:
And here they go missing:
Even though that's the same version # of the JAR file.